The secret is in the sludge

This paper shows how to improve anaerobic digester start-up performance through use of purpose designed biological commissioning procedures. Key data and features for the presented examples are discussed.

i) Using directed sludge adaptation at pilot plant scale the sustainable loading rate for anaerobic digestion of fat, oil and grease (FOG) was increased from 0.7 kg FOG/m3 digester/day (standard co-digestion conditions) to up to 2.1 kg FOG/m3 digester/day (6.5 kg COD/m3 /day) when FOG was the sole carbon and energy source.

(ii) Through seed sludge selection using sediment from a wastewater treatment pond receiving boiling hot sugar cane molasses distillery waste (90 -100 oC, pH 4 – 4.5) CPG designed a digester start-up program to achieve full thermophilic treatment at 55-65 oC within 10 days. This design (10,000 m3 digester) replaced a 40,000 m3 mesophilic system reducing the system footprint and construction costs.

(iii) CPG was engaged by the Christchurch City Waste Water Treatment Plant (CWTP) in 2010 to commission their two new thermophilic sludge digesters (temperature of 55-60 oC) using digested mesophilic sludge as start material. An active, stable thermophilic sludge culture (7000 m3 ) was produced on full scale within 40 days. The sludge digestion (16 days HRT) with the thermophilic sludge culture achieved improved biogas yield, biosolids stabilisation and VS destruction efficiency while mixed liquor VFA levels remained below 1000 ppm